Opening the terahertz window with integrated diode circuits

The terahertz region of the electromagnetic spectrum, spanning from 100 GHz through 10 THz, is of increasing importance for a wide range of scientific, military and commercial applications. This interest is spurred by the unique properties of this spectral band and the very recent development of convenient terahertz sources and detectors. However, the terahertz band is also extremely challenging, in large part because it spans the transition from traditional electronics to photonics. This paper reviews the importance of this frequency band and summarizes the efforts of scientists and engineers to span the "terahertz technology gap." The emphasis is on solid-state circuits that use nonlinear diodes to translate the functionality of microwave technology to much higher frequencies.     

A 5 mW and 5% efficiency 210 GHz InP-based heterostructure barrier varactor quintupler

This letter reviews the design, construction, and measurement of a 210 GHz heterostructure barrier varactor frequency quintupler. The quintupler utilizes planar heterostructure barrier varactors (HBVs) based on the InGaAs/InAlAs/AlAs material system and has produced a measured output power of 5.2 mW with 5.2% conversion efficiency at 210 GHz. This performance is comparable to the state-of-the-art results reported in the literature for HBV frequency triplers operating at millimeter and submillimeter wavelengths.     

Resonant metal-mesh bandpass filters for the far infrared

The spectral performance of freestanding resonant metal-mesh bandpass filters operating with center frequencies ranging from 585 GHz to 2.1 THz is presented. These filters are made up of a 12-μm-thick copper film with an array of cross-shaped apertures that fill a circular area with a 50-mm diameter. The filters exhibit power transmission in the range 97-100% at their respective center frequencies and stop-band rejection in excess of 18 dB. The theoretically predicted nondiffracting properties of the meshes are experimentally verified through high-resolution beam mapping. Scalability of the filter spectra with mesh dimensions is demonstrated over a wide spectral range. Several modeling methods are considered, and results from the models are shown.     

Identification and Field Evaluation of Grape Shoot Volatiles Attractive to Female Grape Berry Moth (<Emphasis Type="Italic">Paralobesia viteana</Emphasis>)

Solid-phase microextraction (SPME) and gas chromatography coupled with electroantennographic detection (GC-EAD) were used to identify volatile compounds from shoots of riverbank grape (Vitis riparia) that attract the female grape berry moth (GBM, Paralobesia viteana). Consistent EAD activity was obtained for 11 chemicals: (Z)-3-hexen-1-yl acetate, (E)-linalool oxide, (Z)-linalool oxide, nonanal, linalool, (E)-4,8-dimethyl-1,3,7-nonatriene, methyl salicylate, decanal, beta-caryophyllene, germacrene-D, and alpha-farnesene. In flight-tunnel tests that involved female GBM and rubber septa loaded with subsets of these 11 compounds, we found that both the 11-component blend and a seven-component blend, composed of (E)-linalool oxide, (Z)-linalool oxide, nonanal, (E)-4,8-dimethyl-1,3,7-nonatriene, decanal, beta-caryophyllene and germacrene-D, elicited equivalent levels of upwind flight as freshly cut grape shoots. The removal of any of the seven compounds from the seven-component blend resulted in a significant decrease in female upwind flight responses. In a field trial with these two synthetic blends, traps equipped with either blend captured more female GBM compared to traps baited with hexane only (control), although the number of females caught was generally low. There were no differences in the number of males captured among treatments. Although in flight-tunnel trials, moths readily flew upwind to both grape shoots and rubber septa loaded with the best lures, they landed on shoots but not on rubber septa. Coupled with relatively low field catches, this suggests that additional host finding cues need to be identified to improve trap efficacy.     

Integrated GaAs Schottky mixers by spin-on-dielectric wafer bonding

A novel wafer bonding process has been used to integrate high quality GaAs devices on quartz substrates. The method of adhesion by spin-on-dielectric temperature enhanced reflow (MASTER) uses a spin-on-dielectric as a bonding agent to achieve a robust bond that in no way degrades either high frequency performance or reliability. A 585 GHz integrated mixer fabricated using this process has achieved record double-sideband mixer noise temperatures of 1,150 K at room temperature and 880 K at 77 K. Furthermore, the integrated mixers require no mechanical tuning, are easy to assemble, and repeatable. Precise control of the circuit geometry, coupled with the reduction of parasitic elements, allows greater accuracy of computer simulations and will therefore lead to better high frequency performance and bandwidth. This new technology is easily extended to other circuit designs and will allow the development of a new generation of submillimeter-wave integrated circuits     

The Mott diode as a heterodyne receiver element

This paper considers a novel doping profile for Schottky barrier mixer diodes called the Mott barrier. The structure consists of a metal-semiconductor junction in which the semiconductor's epitaxial layer is very lightly doped and thin enough so that it remains depleted even under substantial forward bias. It has been proposed that Mott barrier diodes will generate less noise and have lower series resistance-junction capacitance products than standard Schottky diodes, thus increasing the sensitivity and cut-off frequency of heterodyne receivers. In this paper, the band structure and electron transport properties of the Mott diode are evaluated. This analysis shows that the Mott diode actually will have a large series resistance-junction capacitance product and excessive hot electron noise, making it a poor candidate for high-frequency applications. Experimental results are presented which substantiate these conclusions.     

Terahertz sources and detectors and their application to biological sensing

Terahertz spectroscopy has long been used as an important measurement tool in fields such as radio astronomy, physical chemistry, atmospheric studies and plasma research. More recently terahertz technology has been used to develop an exciting new technique to investigate the properties of a wide range of biological materials. Although much research remains before a full understanding of the interaction between biomaterials and terahertz radiation is developed, these initial studies have created a compelling case for further scientific study. Also, the potential development of practical tools to detect and identify biological materials such as biological-warfare agents and food contaminants, or of medical diagnostic tools, is driving the need for improved terahertz technology. In particular, improved terahertz sources and detectors that can be used in practical spectroscopy systems are needed. This paper overviews some of the recent measurements of the terahertz spectra of biomaterials and the ongoing efforts to create an all-solid-state technology suitable not only for improved scientific experiments but also for military and commercial applications.     

Nonohmic Contact Planar Varactor Frequency Upconverters for Terahertz Applications

The development of tunerless millimeter and sub-millimeter wavelength frequency upconverters with integrated planar varactor circuits is described in this paper. An upconverter operating at 200 GHz is implemented as a proof-of-principle demonstration, and designs using both ohmic and nonohmic contacts are tested. The nonohmic contact facilitates fabrication. Both the ohmic and nonohmic devices produced similar performance. Using the nonohmic cathode contact technique and an air-bridge process, 1.6-THz integrated upconverter circuits are fabricated, and the conversion loss is measured to be approximately 22 dB with 40 muW of output sideband power with a 10-GHz microwave pump. A phase-shift measurement for the 1.6-THz upconverter using a standing wave method is described and used to corroborate the results     

Flight Tunnel Responses of Female Grape Berry Moth (<Emphasis Type="Italic">Paralobesia viteana</Emphasis>) to Host Plants

Semiochemicals play important roles in mate and host recognition of herbivorous insects, such as moths, and flight tunnels have been an effective tool in the identification of these bioactive compounds. However, more work has been carried out on pheromones than on host plant cues, and few examples exist where flight tunnel evaluations of host cues have resulted in a lure that is attractive under field conditions. Our goal was to determine whether the flight tunnel could be used to evaluate the response of a specialist moth, grape berry moth (GBM), to its host plant (grapevines), by incorporating ecological and physiological aspects of GBM biology. We found grape shoot tips and mature leaves were more attractive to female GBM than unripe and ripe berries or flowers. Under optimized flight tunnel conditions, approximately 80% of tested females flew upwind and closely approached or landed on the most preferred target. Mating status, wind speed, the time of day, and the presence/absence of patterns that resemble grape tissues on the top of the flight tunnel all significantly affected the responses of female GBM. Consideration of these factors in flight tunnel assays will aid in the development of a synthetic lure that can be used to monitor female moths in the field.